Motorcars are typically equipped with additional side windows in the rear area of the car body. These side windows are either directly integrated into the car body or form part of rear side doors. If such a window is arranged in a side door, it is typically divided into two sections, namely an approximately trapezoidal section and a triangular section. The trapezoidal section is designed in this fashion because the side window pane can be lowered in this region in order to open the window. The upper edge of the side window is almost always composed of an essentially straight section and a curved section in order to prevent an abrupt transition into the triangular region. The upper edge of the quadrangular section can be considered to be roughly straight. However, this section does not extend parallel to the lower edge due to the shape of the car body. When the side window pane is lowered, this results in the upper edge of the window pane still being visible in the front end of the window slot, while the rear section is significantly lowered below the window slot.
This is acceptable with window panes. However, if the side window is shaded by a window shade, one encounters the problem that the upper edge of the side window shade either projects beyond the lower edge of the window or causes a large gap to remain into which objects may fall. This is of particular importance because children are frequently seated on the rear seats of motorcars and thus the risk of objects being dropped into the interior of the door through the gap is accordingly high.
Consequently, it would be very desirable to provide a window shade assembly which ensures that the upper edge of the window shade web will completely close off the extraction slot in the rear portion of the side window shade. In theory, this can be accomplished by arranging the window shade shaft underneath the lower window edge such that it extends parallel to the upper edge of the window. Such an arrangement is usually not feasible, however, due to the space conditions in the interior of a car door. The design engineer is forced to accommodate the window shade shaft parallel to the lower edge. This arrangement results in a longer vertical dimension of the window shade web in the area that lies toward the front end of the vehicle than in the area that lies toward the rear of the vehicle. When the window shade web is wound up, this means that more material needs to be wound up in the front edge region of the window shade web than in the rear edge region.
In this context, EP 0 111 270 teaches simulating a conical winding shaft. The disclosed winding shaft actually has a strictly cylindrical shape and the desired conicality is achieved by providing the window shade web fixed on the winding shaft with a triangular extension. The triangular extension is configured integrally with the section that can be unwound from the winding shaft. The extension is limited by a dividing line that lies parallel to the winding shaft and delimits the extension from the section that can be unwound. The extension is also limited by two lateral edges that respectively originate at the dividing line such that a right triangle is formed, one leg of which consists of the dividing line.
However, this arrangement is limited to applications in which the short lateral edge that forms an extension of the front lateral edge of the window shade, web and thus the other leg of the triangle is shorter than the circumference of the winding shaft. Otherwise, the point would uncontrollably fold over during the wind up process at the assembly site. In addition, the strip shaped blanks are difficult to handle during assembly due to the limited reproducibility. One also has to take into account that the winding shaft ultimately moves along an arc of a circle when the triangular compensating section is wound up. In this case, the radius of the arc is defined by the length of the compensating section and the tip of this compensating section. The lack of rigidity in the material used for the window shade web additionally complicates the situation.
Another solution to this problem is disclosed in FR 2 750 158. In that reference, the conical shape of the winding shaft is achieved by wrapping up a triangular patch on a cylindrical core element. The patch is wound up with the long leg first. Although the reproducibility is somewhat improved with this arrangement, it is necessary to handle two separate blanks.